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Primax Tools

Percentage Calculator

Solve the five most common percentage questions, with the working shown so you can trust and reuse the result.

Runs entirely in your browser. Nothing is uploaded.

X% of Y

Enter both values to see the result.

X is what % of Y

Enter both values to see the result.

Percentage increase

Enter both values to see the result.

Percentage decrease

Enter both values to see the result.

Percentage difference

Enter both values to see the result.

Which one do I need?

Use increase/decrease when one value is the starting point. Use difference when comparing two values with no natural baseline, such as two prices or measurements.

Step by step

How to use the Percentage Calculator

  1. 1

    Pick a calculation type: X% of Y, X is what % of Y, increase, decrease or difference.

  2. 2

    Enter the two values.

  3. 3

    Read the result and the step-by-step explanation.

  4. 4

    Copy the result with one click.

What it does well

Five modes

Covers percentage of a number, percentage share, increase, decrease and symmetric difference.

Explained working

Each answer shows the formula with your numbers substituted in.

Precise decimals

Results are shown to sensible precision without floating-point noise like 0.30000000000000004.

Input validation

Division by zero and non-numeric values are caught and explained.

Who uses it

Shoppers
Work out the real saving on a 35% discount or compare price changes.
Analysts
Report month-over-month growth and the percentage difference between two measurements.
Students
Check homework answers and learn the formula behind each type.

Increase, decrease and difference are not the same

Percentage change compares a new value with an original value: (new minus old) divided by old, times 100. Going from 80 to 100 is a 25% increase, but going from 100 back to 80 is a 20% decrease, because the base changed. This asymmetry surprises many people and is why a 50% loss needs a 100% gain to recover.

Percentage difference is used when neither value is the reference, for example two lab measurements or two shop prices. It divides the absolute difference by the average of the two values, giving the same answer whichever order you enter them. For 80 and 100 the percentage difference is 22.22%.

Quick mental shortcuts

X% of Y equals Y% of X, so 8% of 50 is the same as 50% of 8, which is 4. To find 10%, move the decimal point one place left; 5% is half of that, and 15% is the two added together. These tricks are handy for estimating tips and discounts before checking with the calculator.

Frequently asked questions

How do I calculate a percentage increase?

Subtract the original value from the new value, divide by the original value and multiply by 100.

Why can the decrease mode give a negative result?

If the new value is higher than the original, it was actually an increase, which the explanation points out.

How many decimals are shown?

Up to four decimal places, with trailing zeros removed.

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